This invention relates, in general to semiconductors, and more particularly, to a method for making a self-aligned impurity induced disordered (IID) structure for semiconductors.
In III-V compound semiconductor devices such as light emitting diodes (LED), lasers, and heterojunction bipolar transistors, minority carrier confinement and isolation from high recombination surfaces is critical to device performance. An ability to vary band-gaps in III-V compound semiconductor materials such as aluminum gallium arsenide (AlGaAs) by adjusting the aluminum (Al) and gallium (Ga) mole fractions during crystal growth allows for minority carrier confinement in a vertical direction and is a common practice. Minority carrier confinement, however, also needs to be controlled at lateral edges of the semiconductor device. A variety of lateral current confinement approaches such as laterally restricted current injection and multiple epitaxial regrowth processes have been tried to reduce these lateral minority carrier confinement problems. However, laterally restricted current injection does not scale down as lateral active dimensions approach twice a diffusion length of minority carriers (.about.10 microns), and multiple regrowth procedures suffer from process complexity. Additionally, regrowth over a substrate containing a high percentage of aluminum have acute problems due to oxide formation which inhibits epitaxial nucleation. All approaches to date have proved to be unsatisfactory for use in a manufacturing environment.
Work discussed and done by W. D. Laidig, N. Holyonak, Jr., M. D. Camras, K. Hess, J. J. Coleman, P. D. Dapkus, and J. Bardeen, "Disorder of an AlAs-GaAs Super Lattice by Impurity Diffusion," Applied Physics Letters 38 (10), May 15, 1981, pages 776-778 and R. L. Thornton, W. J. Mosby, and H. F. Chung, "Unified Planar Process for Fabricating Heterojunction Bipolar Transistors and Buried-Heterostructure Lasers Utilizing Impurity-Induced Disordering," Applied Physics Letters 53 (26), Dec. 26, 1988, pages 2669-2671 both describe using diffusion of dopants into aluminum gallium arsenide structures. These articles demonstrate that by diffusion of Group IIB and Group IVA, zinc and silicon respectively, into an aluminum gallium arsenide interface or active area allows for the localized interdiffusion of aluminum (Al) and gallium (Ga). A thin active device layer, of typically low Al content, surrounded by cladding layers of typically high Al content, could be converted selectively by a laterally restricted diffusion to a wider band-gap higher Al content material. This process allows the formation of isolated narrow band-gap regions of semiconductor `active` material to be completely surrounded by single crystal wide band-gap material which forces minority carrier confinement to the narrow band-gap `active` material and prevents minority carriers from reaching infinite recombination velocity surfaces where they would be lost. This process has been called Impurity Induced Disordering (IID). Typical fabrication of an IID structure has several problems. First, Group IIB and Group IVA dopants are generally diffused from a top surface to an active area which is approximately 1.0 to 2.0 microns in depth or distance. As a result of these long diffusion distances long periods of time at high temperatures are required to drive the Group IIB and Group IVA dopants to a desired depth and location. Second, spreading of the dopants leads to a Gaussian distribution which does not allow accurate alignment of dopants to a selected target area. Therefore, a method that enables a self-aligned lateral diffusion to produce an IID structure that controls lateral minority carrier confinement and isolation of free recombination surfaces is highly desirable.